EMPTY SUBTITLE LAYER	;D
If you need to alternate subtitle tracks, use a "blank" subtitle track (save and compile a subtitle track with no entries in it) as the first subtitle track, then add the actual subtitles as an additional subtitle track. You can turn the subtitles on at the beginning -- and you never have to turn subtitles on or off -- you just leave them on all the time. When subtitle track 1 is playing, you don't see anything because there isn't anything there -- but it's easy at any point to switch to subtitle track 2 -- where your subtitles really are.
VERSION: all SUBTITLES SOURCE: Mary K Sizemore